1. Field of the Invention
The present invention relates to a process for the production of resilient cellular materials and more particularly to a process for producing a composite foamed material.
2. Description of the Prior Art
A variety of cellular, and particularly foamed, materials are well known in the prior art. Procedures for the production of such materials have correspondingly been known in the art, as well as procedures for producing composite materials which include foamed or cellular materials. It is recognized that the advantage of a composite material is that it typically displays physical properties which differ from the individual components of the material. Further, the composite may be less expensive than an isolated material due to the inclusion of relatively inexpensive fillers. The present invention provides a composite foamed material, and a process for the production thereof, having particularly advantageous physical characteristics for certain applications.
In U.S. Pat. No. 3,300,421, issued to Merriman et al. on Jan. 24, 1967, there is disclosed a process for the production of "bonded resilient fragment" materials. The Merriam et al. patent discloses a process in which substantially rigid, pre-expanded glass or synthetic resin particles are combined with resilient cellular material and a bonding agent. The cellular material is selected from natural rubber, synthetic rubber and polyurethane. The resultant mix is compressed while substantial bonding occurs. The material produced by the process of the Merriman et al. patent is particularly adapted for certain applications. A cushioning material comprising a mixture of shredded pneumacel batting and shredded particles of polyurethane or rubber bonded together by an elastomeric binder is disclosed in U.S. Pat. No. 3,894,973, issued to Yunan on July 15, 1975.
Generally, both of these patents and the other references fail to appreciate the significant finding of the present invention that a composite of neoprene and polystyrene does not display substantial increase in flammability or smoking over simply the neoprene material. These and all other references also fail to recognize that the minimal increase in these characteristics is obtained while at the same time advantageous physical properties, particularly impact absorption, are achieved with a product which is less expensive than a pure neoprene material. Typical prior art for certain applications uses pure neoprene, while the present invention provides a composite material which is less expensive, displays greatly improved impact absorption properties, and does not exceed desired flame and smoke limitations.
In a particular aspect, the Merriman et al. procedure employs already expanded polystyrene granules, which granules are therefore uniform in shape. In contrast, the present invention includes in one embodiment the expansion of polystyrene beads while under compression and while in combination with resilient cellular neoprene, and this produces irregularly-shaped, expanded beads. It has been found that, as a result of this expansion of the polystyrene beads while commingled with the cellular material, a more intimate relationship between the two components is achieved. For example, it has been observed that closely spaced polystyrene beads, when expanded in the preferred embodiment in proximity with the existent cellular material, with trap portions of the cellular material therebetween, which would not result by the process of the Merriman et al. patent. In addition, the compression of the material in accordance with the Merriman et al. patent tends to crush the pre-expanded polystyrene beads, whereas the expansion of the beads after the step of compression and in the presence of the existant cellular material will tend not to produce "crushed" beads, but only to cause the beads to expand in irregular fashion.
A number of other composite foamed materials have been proposed in the prior art. In U.S. Pat. No. 3,607,797, issued to Rubens et al. on Sept. 21, 1979, there is disclosed a composite foam having copolymer particles dispersed throughout a urethane foam matrix. The composite foam of the Rubens et al. patent is prepared by combining expandable copolymer beads with a polyurethane foam precursor, and thereafter allowing the mixture to foam. Similar materials having thermoplastic beads which are expanded with the surrounding and primarily supporting foam material are disclosed in U.S. Pat. Nos. 3,878,133, issued to Rubens on Apr. 15, 1975, and 2,958,905, issued to Newberg et al. on Nov. 8, 1960. In U.S. Pat. No. 3,503,840, issued to Parrish on Mar. 31, 1970, there is disclosed a composite material having closed-cell reinforcing particles supported within a surrounding foam matrix, the closed-cell particles not being expanded with the foam matrix.
Einhorn et al. disclosed in U.S. Pat. No. 3,114,722, issued on Dec. 17, 1963, a composite material comprising shredded cellular material bonded together by a prepolymer binder. Procedures for the production of foamed materials in which polystyrene beads are held together with a binder are disclosed in U.S. Pat. Nos. 3,585,157, issued to Beck on June 15, 1971, and 2,959,508, issued to Graham et al. on Nov. 8, 1960. Additional references in this art include the following: U.S. Pat. Nos. 3,855,049, issued to Klein on Dec. 17, 1974; 3,251,916, issued to Newnham et al. on May 17, 1966; 2,892,216, issued to Steel on June 30, 1959; and 2,878,153, issued to Hacklander on Mar. 17, 1959, as well as Great Britain Pat. Nos. 1,033,702 issued to Oak and 889,278 issued to Taylor.
In none of these references is there described the expansion of the polystyrene beads in situ with open celled material and binder maintained under pressure. More generally, the present invention achieves a product in another aspect which incorporates polystyrene material but which surprisingly does not have the disadvantageous smoking and flammability characteristic of polystyrene.